They are told point-blank that their 20-inch "baby" will probably grow into a 20-foot adult and live for 25 years. That's a lot of mice, rats, rabbits, and chickens to feed an adult snake capable of quickly dispatching other beloved pets, children, or even adults.

Authorities in South Florida suspect that many frustrated or frightened Burmese python owners have been releasing their snakes into the nearby Everglades rather than trying to find a new home in captivity for them.

The result: a significant population of Burmese pythons has taken up residence near the top of the food chain in Everglades National Park. And they are breeding.

Walter Meshaka, a leading authority on nonnative reptiles and amphibians in the US, likens the Burmese python situation in the Everglades to a "runaway train." If left unchecked, these big snakes might become a "candidate for top predator of the Everglades," he says.

Two confrontations have highlighted the battle between python and alligator for preeminence. A few years ago a group of park visitors watched a gator and a python locked in a vicious struggle to eat each other. It ended in a draw, with both animals retreating – after 70 hours of combat.

Last year, researchers discovered a 13-foot python that had swallowed a six-foot alligator. But the snake had bitten off more than it could handle. Both animals died.

Burmese pythons are native to Southeast Asia and have no known predators in North America. They are considered one of the hottest "exotic" pets and are being shipped into the US by the thousands. Once here, there are no regulations on who can breed, sell, or own them.

Scott Harden of the Florida Fish and Wildlife Conservation Commission says his agency is drafting new rules that would require Burmese python owners to be at least 18 years old and obtain a permit that would match an implanted tag in the animal. The rule is designed to discourage snake dumping.

The threat to humans from the massive snakes remains low, Mr. Harden says, but they could eliminate entire populations of endangered rodents and other species. Other experts say the snakes pose a serious threat to children and pets.

Burmese pythons have three rows of sharp teeth and powerful jaws. They hide in grass or brushes and unleash a lightning-fast bite to immobilize their prey. Then they coil around the prey's chest and neck to prevent them from breathing.

Scientists in Everglades National Park are using a beagle, nicknamed "Python Pete" to sniff out the unwanted intruders. The researchers have also implanted tracking devices in seven captured snakes. They are hoping that during the January to March mating season the implanted snakes will lead them to others.

In 2005, 95 snakes were captured in the Everglades. So far this year, more than 154 have been picked up.

No one is sure how many Burmese pythons are out there. But the population is healthy and increasing. The largest snake captured so far in the Everglades was 16 feet long and weighed 150 pounds.

One of the largest Burmese pythons on record is a snake that died earlier this year at an Illinois zoo. The 29-year-old snake named "Baby" was 27 feet long and weighed 403 pounds, according to a report in the Chicago Daily Herald.

"They are pretty adaptive creatures, and they are eating just about everything from a small bobcat to a variety of birds," says Ms. Friar of the Everglades park.

Despite the increasing effort, many experts are not optimistic about the chances of eliminating pythons from the Everglades.

"We have been remarkably unsuccessful in eradicating any firmly established alien species in Florida," says Richard Bartlett, a reptile expert in Gainesville, Fla.

"There are probably 50 to 60 species of lizards, frogs, snakes, a couple of turtles, and a crocodilian that are firmly established here," he says. "Try though we might to get rid of them, we generally give up."

To Mr. Meshaka, it is a question of ethics. "I think we are better human beings when we take good care of the world around us," he says. "But when we see this accumulation of exotic species – whether it is birds, or fish, or plants, or [reptiles and amphibians] – it is a barometer of our failure to be good stewards."